Switching voltage regulators generate an output voltage from an input voltage and are implemented with active components such as a pulse width modulation controller (PWM), driver, power MOSFETs, and passive components such as inductors, transformers or coupled inductors, capacitors, and resistors. Controllers typically measure the output current and output voltage in order to regulate and monitor the output voltage. Measuring the input current and input voltage allow the controller to improve regulation and monitoring, as well as monitoring input power for voltage, current, and power constraints.
Knowledge of the regulator input current and voltage is required in some controllers for improved regulation algorithms and monitoring input power for voltage, current, and power constraints. Measuring the input current and voltage requires external and internal sense circuitry in the controller. However, components in the sensing network may drift over time which introduces offset errors. The input voltage and operating temperature can also change, introducing further offset errors. Additional offset error can be introduced when the load is applied (active).
Calibration can be used to account for offset errors. However, offset calibration requires the sensed input signal to be zero which may not be guaranteed during system run time i.e. when the load is applied (active). Accordingly, components with very high precision and accuracy with the lowest temperature drift are conventionally in place of performing offset calibration. These kind of components are not standard and therefore increase overall cost. Another conventional approach involves performing offset calibration only when the regulator system is off. However, some regulator systems never turn off meaning that the error introduced by component drift during run time is never addressed. Also, some regulator systems recycle power infrequently and the sense circuit component values may have drifted before the next power cycle. A cost-effective calibration technique and circuit which can be used during voltage regulator run time is therefore desirable.